Previous studies of marrow transplantation for myelodysplasia (MDS) performed in Seattle have shown that using cyclophosphamide (Cy) plus 12 Gy total body irradiation (TBI), 45% of patients achieve long-term disease-free survival. In patients without excess blasts, transplant- related toxicities were the most common reasons for failure, while in patients with excess blasts relapse was the most common problem. In this project, we propose to test, in patients with MDS without excess blasts, whether substitution of busulfan (Bu) for TBI can reduce transplant- related mortality without causing an increase in relapse frequency. In patients with MDS with excess blasts, we plan to study whether a preparative regimen which combines Bu with Cy and TBI can reduce the relapse rate without an increase in toxic deaths. Previously many patients with MDS were judged not to be candidates for marrow transplantation either because of age or because they lacked an appropriate donor. In this proposal, we plan to explore marrow transplantation for Mds in patients up to age 65 and in patients using unrelated matched or partially matched donors.